The article is very broad and addresses a number of issues that have been on-going withing the industry. For example, they have already developed a standard for 3G femto cells (indoor; connected through 3rd party backhaul to operator's network). For outdoor cells, the interface can be the same as that of any other type of cell. There's also the issue of coordination with macrocells which is a feature of LTE Release 10. I think the critical part will be tackling the logistical issues to deploy small cells in large numbers and this is a tricky issue as it varies significantly depending on municipality. Another issue is ensuring low cost for small cell deployments... For more information, see: http://frankrayal.com/small-cells-backhaul/